Generally, since portable wireless power transmission devices such as mobile phones, PDA, PMP, DMB terminals, MP3 or notebook computers are not supplied with a conventional household power source since users use the portable wireless power transmission devices while moving around. Therefore, it is necessary to install disposable batteries or rechargeable batteries in the portable wireless power transmission devices.
However, as a charger for charging electricity in a battery pack for these wireless power transmission devices, there is a terminal supply system in which electricity is received from a conventional power source and a power source is supplied to a battery pack via power supply lines and a power supply terminal. However, where the battery pack is attached/detached to/from the charger when a power source is supplied to this terminal supply system, an instant discharge phenomenon occurs due to the different potential difference of terminals disposed in both sides of the battery pack. Therefore, the battery pack has an increasing possibility to start fires as foreign substances are accumulated in the terminals. Also, since the terminals are directly exposed to the air, the life span and performances of the charger and the battery pack may be deteriorated, for example, due to the spontaneous discharge in the presence of moisture or dusts.
In order to solve these problems regarding the terminal supply system, there has been developed a wireless charger. That is to say, this conventional wireless charger is charged by a secondary coil of the battery when a portable terminal block having a battery pack mounted inside is disposed upwardly in a primary coil of wireless charger. That is to say, an induced electromotive force is generated in the secondary coil by the magnetic field formed in the primary coil, and electricity induced from the induced electromotive force is charged in the secondary coil.
However, these conventional wireless chargers have no practical use since it is possible only to supply a power to a portable terminal block, but they have difficulty in use for other applications.
Furthermore, the wireless charger may be damaged due to the increased loss of power in the primary coil with the changes in the magnetic field when metals are disposed adjacent to the magnetic field generated in the primary coil.